mac80211: RCU-ify STA info structure access

This makes access to the STA hash table/list use RCU to protect
against freeing of items. However, it's not a true RCU, the
copy step is missing: whenever somebody changes a STA item it
is simply updated. This is an existing race condition that is
now somewhat understandable.

This patch also fixes the race key freeing vs. STA destruction
by making sure that sta_info_destroy() is always called under
RTNL and frees the key.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/net/mac80211/debugfs_sta.h b/net/mac80211/debugfs_sta.h
index 574a1cd..8b60890 100644
--- a/net/mac80211/debugfs_sta.h
+++ b/net/mac80211/debugfs_sta.h
@@ -1,6 +1,8 @@
 #ifndef __MAC80211_DEBUGFS_STA_H
 #define __MAC80211_DEBUGFS_STA_H
 
+#include "sta_info.h"
+
 #ifdef CONFIG_MAC80211_DEBUGFS
 void ieee80211_sta_debugfs_add(struct sta_info *sta);
 void ieee80211_sta_debugfs_remove(struct sta_info *sta);